The present invention relates to electrophotographic printing machines, and more particularly to a tracking system for laterally moving belts in electrophotographic printing machines.
Color registration in electrophotographic printing machines requires that images are precisely registered in the lateral direction. As an endless photoreceptor belt or intermediate transfer belt turns around a set of rollers similar to a continuous conveyer belt, there is typically an undesired motion of the belt that occurs back and forth in the lateral direction of the belt travel. This lateral belt motion is caused by lateral forces that are generated by misalignment of the rollers as well as belts that are conical (one belt edge longer than the other) and rolls that do not have constant diameters. Heretofore, one solution to the problem of lateral belt motion was addressed by using stationary edge guides and low lateral force rolls wherein fixed edge guides are located on either side of the belt to prevent it from walking off the rolls completely. These edge guides supply an equalizing force to that generated by the misshapened belt and misaligned rollers. However, in using stationary edge guides, the belt will still move back and forth according to the contour profile of the belt edge. When this type of belt guidance system is used in a single pass color xerographic application, the lateral belt motion due to the belt edge profile causes a misregistration of the colors.
A feature of the disclosed embodiment is an apparatus for tracking belts in an electrophotographic printing machine. That includes an actuated (i.e. movable) edge guide system that operates in combination with a belt edge sensor, a belt hole sensor and low lateral force rollers. The P/R, or IBT module is racked (making the long axis of the rollers not parallel) slightly so that the belt has a tendency to walk toward the edge guide. The profile of the belt edge is learned as a function of belt position. This is accomplished by the use of an encoder and a belt hole sensor. Once the belt edge profile is learned, the encoder, belt edge sensor and belt hole sensor are used to actuate the edge guiding system to compensate for the contours of the belt edge. The movement of the edge guide will be prescribed to mimic the belt edge profile, which will result in a constant force being applied on the belt. In this way, a constant lateral position of any given point on the belt can be maintained.
The following Xerox Corporation U.S. patents disclose some examples of belt tracking apparatus. U.S. Pat. Nos. 3,500,694, 5,510,877, 6,137,517, 6,141,526 issue to Ikeda discloses a color printer belt meander control method.
All the references cited herein are incorporated by reference for their teachings.